GAWK: Effective AWK Programming

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168 GAWK: Effective AWK ProgrammingIf a translation of gawk’s messages exists, then gawk produces usage messages, warnings,and fatal errors in the local language.
Chapter 10: Advanced Features of gawk 16910 Advanced Features of gawkWrite documentation as if whoever reads it is a violent psychopath who knowswhere you live.Steve English, as quoted by Peter LangstonThis chapter discusses advanced features in gawk. It’s a bit of a “grab bag” of itemsthat are otherwise unrelated to each other. First, a command-line option allows gawk torecognize nondecimal numbers in input data, not just in awk programs. Next, two-wayI/O, discussed briefly in earlier parts of this book, is described in full detail, along withthe basics of TCP/IP networking and BSD portal files. Finally, gawk can profile an awkprogram, making it possible to tune it for performance.Section C.3 [Adding New Built-in Functions to gawk], page 287, discusses the ability todynamically add new built-in functions to gawk. As this feature is still immature and likelyto change, its description is relegated to an appendix.10.1 Allowing Nondecimal Input DataIf you run gawk with the ‘--non-decimal-data’ option, you can have nondecimal constantsin your input data:$ echo 0123 123 0x123 |> gawk --non-decimal-data ’{ printf "%d, %d, %d\n",> $1, $2, $3 }’⊣ 83, 123, 291For this feature to work, write your program so that gawk treats your data as numeric:$ echo 0123 123 0x123 | gawk ’{ print $1, $2, $3 }’⊣ 0123 123 0x123The print statement treats its expressions as strings. Although the fields can act as numberswhen necessary, they are still strings, so print does not try to treat them numerically.You may need to add zero to a field to force it to be treated as a number. For example:$ echo 0123 123 0x123 | gawk --non-decimal-data ’> { print $1, $2, $3> print $1 + 0, $2 + 0, $3 + 0 }’⊣ 0123 123 0x123⊣ 83 123 291Because it is common to have decimal data with leading zeros, and because using itcould lead to surprising results, the default is to leave this facility disabled. If you want it,you must explicitly request it.Caution: Use of this option is not recommended. It can break old programs very badly.Instead, use the strtonum function to convert your data (see Section 5.1.2 [Octal andHexadecimal Numbers], page 75). This makes your programs easier to write and easier toread, and leads to less surprising results.
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